开始刷leetcode day20：Binary Tree Inorder Traversal

Given a binary tree, return the inorder traversal of its nodes' values.

For example:
Given binary tree {1,#,2,3},

   1    \     2    /   3

return [1,3,2].

Java:

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public List<Integer> inorderTraversal(TreeNode root) {
        List<Integer> list = new ArrayList<Integer>();
        if(root == null) return list;
        inorder(root,list);
        return list;
        
    }
    
    public void inorder(TreeNode root, List<Integer> list)
    {
        if(root == null) return;
        inorder(root.left,list);
        list.add(root.val);
        inorder(root.right,list);
    }
}